This invention relates to a scanning electron microscope.
In particular, this invention relates to a scanning electron microscope in which a vacuum chamber is arranged to allow observation of pieces and/or details of relatively large dimensions, such as bearings and gears.
In scanning electron microscopes, it is known to use a vacuum chamber normally in the form of a cup-shaped body which comprises a lateral aperture for introducing the pieces to be examined, and which is disposed at the base of an electronic-optical column normally comprising a plurality of magnetic lenses arranged to focus and control an electron beam emitted by an emitter disposed inside said column.
In known vacuum chambers, said lateral aperture in the cup-shaped body is closed during observations, by a door arranged to cooperate in an air-tight manner, when in its closed position, with a flat surface of said cup-shaped body surrounding said lateral aperture. Said door is normally hinged to said cup-shaped body along one of its lateral edges, in such a manner as to be able to rotate about the vertical axis of a hinge normally provided on a plate removably connected to the cup-shaped body, and hinged to one side of said door.
In the known electron microscopes as heretofore described, the piece to be observed is normally connected to the inner surface of said door by means of a piece holder, which is normally able to enable the piece under examination to be moved from the outside along at least three axes in order to enable successive observation of a plurality of zones on the piece.
One of the most important drawbacks of the known electronic microscopes as heretofore described is that they allow pieces only of relatively small dimensions to be observed, as a large part of the free space inside the vacuum chamber is occupied by the piece holder, which generally projects in cantilever manner from the inner surface of the rotatable door. This drawback can obviously be solved by constructing chambers of greater volume. However, such a design would lead to generally high expense deriving not only from the greater chamber dimensions, but also from the greater complexity of the suction systems which generate the vacuum inside the chamber, and the solution of structural stability and air-tightness problems which arise as a result of using a rotatable door of obviously greater size, the hinge of which would be subjected to torsion stresses by the weight of the pieces under examination, and in particular by the weight of the piece holder.